All Big Six ARP Main Studs/Oil pump clearance

Relates to all big sixes

jrbuckne1

Active member
I wanted to share the problem and fix of running ARP main studs and the new standard flow melling pump clearance problem. The main studs in the ARP kit were too high for oil pump clearance and the oil pick up tube didn't have threads to grab. I called ARP and got two
Bolts sent to me (reference pics for part numbers). I used a felpro gasket as they were much thicker and used a small die grinder to take some material off the oil pump (hopefully not enough to cause it to fail. Im going to the hardware store to get 2 washers and a new nut for the pickup as the old one is not the right threads. Hope this helps someone
 

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F-250 Restorer

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This is why people come to the forum—to find answers and help. It was considerate of you to post how you tackled the problem. I have heard this issue mentioned before. I Believe that Pmuller6 had the same problem.

I think that his post should be part of the pre material of this forum, on permanent display for others to easily find.
 

pmuller9

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I had to grind the stud almost flush with the nut.
Make an .060" aluminum spacer plate under the oil pump.
The oil pump body also got a notch to clear the stud nut.

oil pump clearance.jpg
 

Pontus

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Supporter 2021
Would it really hurt anything to just use a normal main cap bolt for that position? I was going to go with ARP studs too, but is there a normal replacement bolt available of the same quality?
 
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falconcritter

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This is the same for the small 6 as well ! I have the same problem with my 200 block !
 

chessterd5

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Would it really hurt anything to just use a normal rod cap bolt for that position? I was going to go with ARP studs too, but is there a normal replacement bolt available of the same quality?
No it would not hurt anything to use the stock MAIN cap bolt in that location.
The stock bottom end is generally considered reliable to 7 grand. And you don't want to push the crank past 5500 rpm anyway.
And no, I don't think there is a replacement bolt available for the same quality.
 

pmuller9

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Would it really hurt anything to just use a normal main cap bolt for that position? I was going to go with ARP studs too, but is there a normal replacement bolt available of the same quality?
ARP makes regular bolts of the same quality. See their 2021 catalog starting on page 113 there are 11 pages of bolts listed.
If you read the first post, ARP sent two bolts to replace the two studs.
If you want to use ARP bolts instead of studs they are available as separate items.
 

Pontus

Well-known member
Supporter 2021
After searching for new cap bolts and coming up bupkis (other than some NOS on ebay for $20), my search came up with a result here (as it so often does) saying there's no problem with reusing the old bolts, so I think I'll save myself $100 and potentially having to line bore my mains according to a machinist report from CNC-Dude. And the same post makes me think that I wouldn't want to have different clamping pressure on one main from a fine threaded stud on one side to a course, stock bolt on the other, so perhaps mixing them wouldn't be that great? Although that probably only relates to race engines, not a sub 4krpm tractor motor.

ARP makes regular bolts of the same quality. See their 2021 catalog starting on page 113 there are 11 pages of bolts listed.
If you read the first post, ARP sent two bolts to replace the two studs.
I had seen and looked up those bolts, but the one in question is just a slightly shorter stud that still interferes since he had ground off a lot more than 0.021" from the pump housing.
 
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pmuller9

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After searching for new cap bolts and coming up bupkis (other than some NOS on ebay for $20), my search came up with a result here (as it so often does) saying there's no problem with reusing the old bolts, so I think I'll save myself $100 and potentially having to line bore my mains according to a machinist report from CNC-Dude. And the same post makes me think that I wouldn't want to have different clamping pressure on one main from a fine threaded stud on one side to a course, stock bolt on the other, so perhaps mixing them wouldn't be that great? Although that probably only relates to race engines, not a sub 4krpm tractor motor.


I had seen and looked up those bolts, but the one in question is just a slightly shorter stud that still interferes since he had ground off a lot more than 0.021" from the pump housing.
It's not the stud length that is the problem.
The nut that is used on the stud is taller than a bolt head plus the nut sits on a washer which raises it even higher.

You can certainly reuse the stock bolts on a naturally aspirated engine that is running below 5500 rpm.
The original poster is building a turbocharged engine where it is a good idea to use a better bolt or stud on the main caps and cylinder head and is why this thread was started

You can use the ARP bolts (not studs) for the main caps as replacement.
Since they will have the same thread pitch as the stock bolts the clamping force will be the close to the same.
I would use a complete set and not mix bolts.
 
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guhfluh

Famous Member
No it would not hurt anything to use the stock MAIN cap bolt in that location.
The stock bottom end is generally considered reliable to 7 grand. And you don't want to push the crank past 5500 rpm anyway.
And no, I don't think there is a replacement bolt available for the same quality.
Please provide proof of a stock bottom end being reliable to 7000rpm or a crank problem at 5500rpm. Thanks.
 

chessterd5

Well-known member
Please provide proof of a stock bottom end being reliable to 7000rpm or a crank problem at 5500rpm. Thanks.
I was referring to the stock hardware Screenshot_20210331-133807.pngScreenshot_20210331-133515.png
You're already at 3,650 fpm at 5500 rpm. In a stock engine.
I didn't say a crank failure per se. I said you didn't want to push a crank past 5500 rpm anyway. Unless you wish to make improvements on the positive crankcase ventilation system.
Elvis has left the building.
 

guhfluh

Famous Member
I was referring to the stock hardware View attachment 6065View attachment 6066
You're already at 3,650 fpm at 5500 rpm. In a stock engine.
I didn't say a crank failure per se. I said you didn't want to push a crank past 5500 rpm anyway. Unless you wish to make improvements on the positive crankcase ventilation system.
Elvis has left the building.
So then, even by your calculations, it is NOT safe for a stock bottom end Ford 300 to rev to 7000rpm.

What does the PCV system have to do with stock cranks?
 
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drag-200stang

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It could meet Elvis, if the drive shaft all adds up on the short side, best to check , but to long is not good either.
 

THE FRENCHTOWN FLYER

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< My 147 mph S/P car has all exotic parts - except for the aforementioned stock main cap bolts.

My Frenchtown Family Truckster has a stock crank, oil system, rods, rod bolts and hypereutectic pistons. It has - dunno - maybe 1300 - 1400 quarter mile passes on it. I'm not near my logbook. Driver shifts at 5200-5500 depending on how fast we want it to run.
 

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THE FRENCHTOWN FLYER

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My Frenchtown Family Truckster has a stock crank, oil system, rods, rod bolts and hypereutectic pistons. It has - dunno - maybe 1300 - 1400 quarter mile passes on it. I'm not near my logbook. Driver shifts at 5200-5500 depending on how fast we want it to run.
EDIT: 1366 quarter mile passes. We've only had one issue with the lower end when it lost oil pressure due to a failed oil pump pickup gasket. The camshaft has also been upgraded to a roller cam.
 

guhfluh

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EDIT: 1366 quarter mile passes. We've only had one issue with the lower end when it lost oil pressure due to a failed oil pump pickup gasket. The camshaft has also been upgraded to a roller cam.
Thank you for the info Greg. My point, especially since this is a sticky thread, is that there needs to be correct info in here and as far as I know there are only three people on these forums to have reported broken a crank (cast or forged), including yourself - none of which were at a magical 5500rpm and zero reports of a stock bottom end, crank, rods, pistons, bolts, pump, caps and block surviving at 7000rpm for any length of time(which if were true would also debunk the claim a crank magically fails at 5500rpm).
 
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